On 2004-09-25 11:43:45 +0200, Michael Holzt wrote: > > I don't understand what problem you and Michael are trying to > > solve with the messages after this one. What doesn't match? > > The old code did not match for single character sub-domains.
Yes, but Robert already fixed that:
On 2004-09-14 08:49:57 -0700, Robert Spier wrote:
| my $subdomain = '(?:[a-zA-Z0-9](?:[-a-zA-Z0-9]*[a-zA-Z0-9]))';
|
| I think what we want is this:
|
| my $subdomain = '(?:[a-zA-Z0-9](?:[-a-zA-Z0-9]*[a-zA-Z0-9])?)';
(and as an indication that the error was a simply typo, I offer that the
second grouping is rather useless without the ? after it).
> > All the examples you provide match fine, assuming we're talking
> > about /^$subdomain(?:\.$subdomain)*$/. The added look-aheads
> > and alternations and other complications don't add anything, as
> > far as I can see.
>
> Oh, they are there for a reason: Because without them we would
> match too much, e.g. illegal subdomains. A subdomain can not
> start or end with a hyphen, and to ensure this, complicated
> regexps like posted are needed.
No, they aren't. Robert's fix is fine. Indeed, if you look at at the
BNF notation
> # sub-domain = Let-dig [Ldh-str]
> # Let-dig = ALPHA / DIGIT
> # Ldh-str = *( ALPHA / DIGIT / "-" ) Let-dig
you can see that it matches the BNF notation exactly:
my $subdomain = '(?:[a-zA-Z0-9](?:[-a-zA-Z0-9]*[a-zA-Z0-9])?)';
<-----------><--------->
*(A/D/"-") Let-dig
<---------><--------------------------->
Let-dig [Ldh-str]
> However it looks to me like the lookahead for the
> digit or char after the hyphen is not needed. We can
> just match it normally. So i submit now the following
> pattern for evaluation:
>
> (?:[a-zA-z0-9]+(?:[a-zA-Z0-9]|-[a-zA-Z0-9])*)
Nope, this is wrong. It doesn't match
xn--bcher-kva
which is a perfectly legitimate domain component (which also happens to
exist, see http://xn--bcher-kva.ch/).
> Btw: Why don't we use case-insensitive matching?
No special reason, I think. When I wrote the regexps, I just literally
translated the BNF to regexps. I was sorely tempted to "optimize" the
regexps, but resisted (mostly) because I wanted to make it easy to
verify that the regexps do indeed implement the BNF.
hp
--
_ | Peter J. Holzer | Je höher der Norden, desto weniger wird
|_|_) | Sysadmin WSR | überhaupt gesprochen, also auch kein Dialekt.
| | | [EMAIL PROTECTED] | Hallig Gröde ist fast gänzlich dialektfrei.
__/ | http://www.hjp.at/ | -- Hannes Petersen in desd
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